Pool is clear but bottom looks spotty and dirty

[BigDave]

Suggestions:

• Get a K2006 kit.
• Read the Best Guess Chlorine page.
• Adjust your chlorine levels to the correct range for algae killing -- use the low end of that range.
• Keep the chlorine there . . . for weeks.
• Begin brushing REGULARLY.
• Do not wear high-fashion expensive swimwear in the pool. Skin is VERY chlorine resistant; women's swimwear that costs over $100 is NOT. Such suits are made to be seen in, not to be swum in. If you use the pool a LOT, all polyester water aerobics suits are super-durable.

Black algae penetrates down into the cracks and crannies of the pool surface. Even when it seems to be gone, it's not. If you keep brushing while maintaining chlorine levels, it will be *mostly* gone 2 weeks after you can't see it any more.

But, it will not be all gone, and will recur if you let chlorine levels go low.

Note that if you have stabilizer levels above 40 ppm, and do not READ and FOLLOW the Best Guess Chart, you're mostly wasting your time. Keep in mind that test strips are HORRENDOUSLY inaccurate when use to measure stabilizer.

I just saw that Ben had provided this advice to someone asking about Black algae. Perhaps we didn't need to go to +shock+ level but other than that we're consistent.
Please resist the urge to "throw stuff at it". Doing so will most likely make it much harder to clean.

[rkrgk]

Thanks BigDave for sending me the post from Ben.
My problem is that the remianing algae does not come off the pool surface at all. I was hoping there is an easier way to make chlorine reach these pores so that there will be progress when I scrub next time.

As I mentioned I did make lot of progress, whatever I could remove with my brush I removed them. And my numbers are not looking that bad (dont know why I dont use much Chlorine overnight with some black algae present still).
This is what I got yesterday evening and this morn.
FC - 8.5 (no change from last night)
pH - 7.8
TA - 150
CH - 400
CYA - 40ppm
Borate - 30ppm

As you can see I also added some Borax thinking it might help me control algae in the long term. I am ading some pics with this. Some of the spots that you see in the pic could be the shadow not the black spots. As you can see the walls and bottom are pretty clear of algae, but there still some.

pool_pic_after_sruubbing1.jpgpool_pic_after_sruubbing2.jpg

[BigDave]

It makes sense that the overnight FC wouldn't change much with so little of the algae's surface area left exposed to chlorine.
I think Borate is a good choice - maybe a little higher. The pH might be getting a tad high (especially with 400 CH). Muriatic Acid is a good way to bring it back down - Be sure to read and understand:Using Muriatic Acid to Safely Lower Your Pool's pH.

[rkrgk]

It makes sense that the overnight FC wouldn't change much with so little of the algae's surface area left exposed to chlorine.
I think Borate is a good choice - maybe a little higher.

Yeah, I was following PoolDocs writeup on increasing to 50ppm, I got only 5 boxes of borax last time, I am planning to add 5 more, thats the reason my pH was a little off too.

The pH might be getting a tad high (especially with 400 CH). Muriatic Acid is a good way to bring it back down - Be sure to read and understand:Using Muriatic Acid to Safely Lower Your Pool's pH.

I did reduce the pH to 7.4 in the last two days.

I also got the polyquat 60 from amazon. And planning to add and see if it makes any difference. and may be get some trichlor powder and sprinkle directly on top of the black spots and brush if I can.

[BigDave]

Sounds like a pretty goo idea - it will lower the pH locally so be on the lookout for pitting in the plaster.

One method I've read is to put the chemical in a zip-loc bag to transport it to the stain then pour / squeeze the slurry onto the target spots.

[rkrgk]

Sounds like a pretty goo idea - it will lower the pH locally so be on the lookout for pitting in the plaster.

Good point,yeah I somehow thought Trichlor is basic, when you mentioned I checked the Taylor booklet,its pH is 2.8-3.5. Hopefully wont stain, I guess I need to take a chance *rock and a hard place*.

One method I've read is to put the chemical in a zip-loc bag to transport it to the stain then pour / squeeze the slurry onto the target spots.

Sounds like a good idea. Let me go check if I can get some Trichlor powder locally here. I have the pucks from last year, but dont have a holder (like this, but got bad reviews.. http://www.amazon.com/Pentair-542068...pentair+holder) or else I could just use it to scratch the floor with it to get same effect I guess. shallow ends I could srub with the puck and see if it makes any difference. I will give it a try and let you know if it makes a difference.

Also do you know why it is bad to use ammonium hydroxide with chlorine in the pool? except that pool is unusable for few weeks. I read somewhere its effective against black algae.

[BigDave]

You could break up a puck and put the chunks over the spots.

I wouldn't advise ammonia products in a pool - PoolDoc or ChemGeek may be able to advise you better - I just don't have the depth or chemistry. I do know that you'd be likely to form chloramines and that monochloramine is an effective algaecide - is does stink and irritate skin. If you want to use the pool, I'd stick with shock FC levels and wear old swimsuits.